1. Field of the Invention
The present invention relates to a radiation imaging apparatus having an electronic cassette and an imaging stand that holds the electronic cassette.
2. Description Related to the Prior Art
In a medical field, a radiation image capturing system, for example, an X-ray image capturing system is constituted of an X-ray generating apparatus for generating X-rays and an X-ray imaging apparatus for taking an X-ray image by reception of the X-rays. The X-ray generating apparatus includes an X-ray source for emitting the X-rays to a patient's body, a source controller for controlling the operation of the X-ray source, and an exposure switch for inputting an emission start command of the X-rays. The X-ray imaging apparatus has an electronic cassette, which receives the X-rays having passed through the patient's body and produces the X-ray image.
The electronic cassette is composed of a flat panel detector (FPD) and a flat rectangular housing containing the FPD. The FPD has a matrix of pixels each of which accumulates signal charge by an amount corresponding to the amount of the X-rays incident thereon. The FPD accumulates the signal charge by a pixel-by-pixel basis, and converts the accumulated signal charge into a voltage signal in its signal processing circuit. Thereby, the FPD electrically detects the X-ray image, and outputs the X-ray image as digital image data.
The electronic cassette is used in a state of being mounted on an imaging stand. Also in some cases, the electronic cassette is used in a state of being put on a bed or held by a patient himself/herself to take the X-ray image of a body part that is hard to take in a stationary state. The electronic cassette is sometimes brought out from a hospital for use in bedside radiography of a home-care patient or in an accident or natural disaster site in an emergency.
Some electronic cassettes are provided with both a wired communicator using a communication line e.g. a cable as a transmission line and a wireless communicator using an electromagnetic wave as the transmission line, in order to transmit and receive various signals including a control signal and an image data signal to and from an external device disposed outside the imaging stand. The wireless communicator is adopted when portability is required of the electronic cassette, for example, in the case of the bedside radiography. The wired communicator is adopted when communication reliability is required, e.g. in the case of using an automatic exposure control (AEC) function. In the AEC function, a dosimeter provided in the electronic cassette measures an X-ray dose passed through the patient's body. When the X-ray dose reaches a threshold value, an emission stop signal is transmitted to the X-ray source to stop X-ray emission. Since delay in transmission of the emission stop signal causes an excessive dose to the patient, the AEC function uses the wired communicator that is superior in transmission stability and transmission speed to the wireless communicator.
In wired communication, as a matter of course, the electronic cassette and the external device are connected through a communication cable, a relay cable, connection terminals, connectors, and the like to establish the wired transmission line. For example, to establish the wired communication between the electronic cassette and the external device, one end of the communication cable is connected through the connector to the connection terminal provided in a side surface of the housing of the electronic cassette, while the other end of the communication cable is connected to the external device. If the electronic cassette is used without being mounted on the imaging stand, all outer surfaces of the housing of the electronic cassette are exposed to the outside, so nothing hinders access to the connection terminal.
On the other hand, if the electronic cassette is used with being mounted on the imaging stand, the imaging stand covers the electronic cassette at least at a part of the side surface of the housing. Thus, when trying to connect the communication cable to the connection terminal of the electronic cassette mounted on the imaging stand, the imaging stand possibly hinders access to the connection terminal, though it depends on the position of the connection terminal, and prevents the connection of the communication cable. In such a case, the electronic cassette is firstly connected with the communication cable, and then is mounted on the imaging stand.
However, when trying to mount the electronic cassette with the communication cable on the imaging stand, the communication cable sometimes interferes with the mounting and needs routing, and brings about a troublesome task. Furthermore, since a magnet the fixed power of which is not so strong is generally used for fixing the connector of the communication cable to the connection terminal of the electronic cassette due to its ease of mating and unmating, the connector is possibly unmated from the connection terminal during the mounting or during moving the imaging stand with the electronic cassette. If radiography is performed without notice of the unmating of the connector from the connection terminal, the AEC function does not work appropriately, so the patient receives an excessive X-ray dose. On the other hand, if the connector is firmly locked in the connection terminal using claws, when the communication cable gets snagged in moving the imaging stand, the connection terminal and the connector easily break.
US Patent Application Publication No. 2011/0110497 discloses a rack and a bed that hold an electronic cassette at their holders. The holder is provided with a connection terminal for connecting the electronic cassette to an external device through a communication cable. When the electronic cassette is held by the rack or the bed, a connection terminal of the electronic cassette is connected to the connection terminal of the holder.
The electronic cassette comes in sizes of 17 inches by 14 inches, 17 inches by 17 inches, and the like, but it is expected to have greater variation in size. Therefore, it is desired that the imaging stand is ready for the electronic cassettes of various sizes. However, the holder of the US Patent Application Publication No. 2011/0110497 is compliant with only a single size of electronic cassette, so another size of electronic cassette cannot be mounted thereon. Even if an incompliant size of electronic cassette is mounted on the holder of the US Patent Application Publication No. 2011/0110497, the center of an irradiation surface of the electronic cassette deviates from the center of an imaging surface of the rack, because the connection terminal is provided in the side surface of the holder.
Japanese Patent Laid-Open Publication No. 2007-007251 discloses an imaging table in which a pair of arms catches opposed side surfaces of a cassette to place the cassette in proper position. Various sizes of cassettes can be mounted on this imaging table. However, this imaging table is designed for a conventional film cassette and IP cassette, and hence is not intended to have a connector for connection to the electronic cassette.